The Aqishan-Yamansu belt in the Eastern Tianshan (Xinjiang, NW China) is an important mineralization belt. The belt mainly comprises Carboniferous volcanic, volcaniclastic and elastic rocks, and hosts many intermediate-felsic intrusions and Fe (-Cu) deposits. The biotite diorite, felsic brecciated tuff, granodiorite and syenite from the western Aqishan-Yamansu belt are newly zircon U-Pb dated to be 316.7 +/- 1.4 Ma, 315.6 +/- 2.6 Ma, 305.8 +/- 1.9 Ma and 252.5 +/- 1.4 Ma, respectively. The mafic rocks (mafic brecciated tuff and diabase porphyry) are tholeiitic to talc-alkaline series, LILE-rich (e.g., Rb, Ba and Pb), HFSE-depleted (e.g., Nb and Ta), and have high Mg-#(44-60), Nb/Ta (15.0-20.0), Ba/La (> 30) and Ba/Nb (> 57) values/ratios, and low Th/Yb ratios (< 1), probably originating from mantle wedge metasomatized by slab-derived fluids. The intermediate-felsic igneous rocks are LILE-rich, HFSE-depleted, with high Sr and Y contents showing typical of normal arc magma affinity. Moreover, the depleted epsilon(Hf)(t) (> 2.10) and positive epsilon(Nd)(t) (> 5.7), combined with variable Nb/Ta ratios (9.52-21.4), Y/Nb ratios (1.47-39.7) and Pb isotopes (Pb-206/Pb-204 = 16.225-17.640, Pb-207/Pb-204 = 15.454-15.520, Pb-208/Pb-204 = 37.097-38.025) suggest that these rocks were magma mixing products between juvenile crustal-derived magmas and minor mantle-derived magmas. Combined published works with our new ages, geochemical and isotopic data, we propose that the Aqishan-Yamansu belt was an Early Carboniferous fore-arc basin during the southward subduction of the Kangguer oceanic slab beneath the Yili-Central Tianshan block. With the continuing southward subduction, the Aqishan-Yamansu fore-arc basin initiated to close, which generated the mafic and intensive intermediate-felsic magmatism associated with regional Fe (-Cu) mineralization.